Excessive heat developed during operation of integrated circuits and particularly very large integrated circuits such as microprocessors, controllers and other high performance electronic logic devices can drastically reduce the reliability and efficiency of the circuit. The increased electronic packaging and power densities of many high performance devices often result in a high heat concentration within a limited area. Dissipation of the excessive heat is critical to prevent damage to or failure of the device. However, the high packaging density of the devices places many constraints on the design of a suitable thermal management system. Finding adequate methods to remove the excess heat has become a very important design parameter in building high performance electronic circuitry.
Many different approaches have been taken to disperse the excess heat that is generated in electronic circuits. One of the most common ways to dissipate the heat is through the use of heat sinks fabricated from extruded aluminum, but aluminum heat sinks have certain physical design limits. One limitation is the shape, which is limited to simple two-dimensional profile shapes that can be extruded. This reduces the potential for developing heat sinks having a reduced size or complex shapes which increase the convective and radiant cooling efficiency of the heat sink.
A new type of heat sink is constructed of filled polymer material that can be injection-molded into a variety of compact, complex shapes which are highly efficient for convective cooling with high velocity forced air. Although the filled polymer material has only about two percent of the thermal conductivity of pure aluminum, these complex-shaped devices have a cooling capacity that is comparable to bulky aluminum heat sinks that cannot fit in a compact, forced convection environment.
To install aluminum or polymer heat sinks, they must be mounted to the device that is to be cooled. This bond is usually accomplished by using mechanical fasteners, compressible pads, silicone grease or conductive epoxies. A major thermal management problem with bonding of these existing heat sinks is a reduction in thermal conductivity across the bond. Also any voids or gaps between the two joint surfaces can easily go undetected and can greatly reduce the thermal efficiency of the joint area.
Other heat sink approaches use liquid-filled pouches or copper-covered sponges compressed between the printed circuit board components and the outside casing of the instrument to transport the heat away from the heat source. The efficiency of the copper covered sponges is limited as heat is transferred only by the copper exterior. Moreover, these heat sinks greatly restrict the airflow through and around the printed circuit board and related chips. As a result, they appear to be limited to only special applications.